#include<stdio.h>
#include<math.h>
int main()
{
	double x1, x2, y1, y2;
	while(scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2) != EOF)
	{
		double s = (x1-x2)*(x1-x2) + (y1-y2)*(y1-y2);
		s = sqrt(s);
		printf("%.2lf\n", s);
	}
	return 0;
}
